According to the currently adopted definition by FAO/WHO, probiotics are: “live microorganisms which when administered in adequate amounts confer a health benefit on the host”. Nowadays, a number of different bacteria are used as probiotics, for example, lactic-acid producing bacteria such as strains of Lactobacillus and Bifidobacteria. Lactic-acid producing bacteria are not only used for their beneficial effect on human or animal health they are also widely used in the food industry for fermentation processes. Often, the microorganisms marketed for these purposes are formulated as freeze-dried powders in a low water content environment.
A general problem encountered in the application of such freeze-dried microorganism preparations is the limited storage stability of the cells since the available free water content is deleterious for the cells. Over time the microorganisms become less viable resulting in high dosages necessity to compensate for this loss of activity, if there are sufficient viable organisms to make this possible.
For the purpose of storage, it is generally known to utilize foil having a plastic layer on one surface on the outside of the compartment, such as a polyethylene laminated aluminum foil as packaging material to reduce exposure of the freeze-dried lactic acid bacteria to moisture and oxygen. But even when barrier materials are effective at restricting the transmission of water molecules through a package, certain features of the package may still allow for the transmission of water molecules, for example, along the edges of a heat-sealed package. Also the process of filling the package in itself may contribute to trapping water inside the packaging.
One solution to maintain a particularly low level of moisture within a package is to incorporate sachets of desiccant material into the internal space of the package to remove the moisture from the headspace of the package. The desiccant material is generally known to reduce the moisture content within a package. Typical desiccant materials are “physical” desiccant materials, such as molecular sieves that bind water molecules within pore spaces of a material. Another type of desiccant material includes hydrate forming agents such as salts, such as ammonium chloride. Desiccant materials may also be used that form no hydrates, such as common salt (NaCl) or potassium bromide (KBr).
Another way to protect freeze-dried lactic acid bacteria cultures is to use an oil-based formulation. Lactic acid bacteria cells have been used in oil-formulations for improved stability of the bacteria, see for example U.S. Pat. No. 4,518,696 by Gehrman et al. The inventors of US patent application publication No. 20050271641 went a step further by adding the step of vacuum-drying the oil before formulation for increased stability of the bacteria cultures and a product called “Reuteri Drops” was manufactured. The product is an oil-based formulation containing L. reuteri made for good stability and shelf life. The unique feature of this production process is a drying step of the oil to remove most of the water. The oil used in US patent application publication No. 20050271641 is a pure edible vegetable oil, preferably sunflower oil. Although oil such as pure sunflower oil would not be expected to contain much water, an unexpected effect of the processing step of drying the oil by placing it under vacuum is a significantly increased stability of the lactobacilli in the formulation.
However there is from time to time still a problem with stability of lactic acid bacteria formulated in oil, which may or may not have been processed by vacuum, as it may not be possible to remove all moisture by vacuum and/or new moisture may enter the oil formulation during packaging or storage in different containers.
The invention described herein fortunately provides an improved and more efficient method for the storage of freeze-dried lactic acid bacteria by combining oil-based formulations containing lactic acid bacteria, for example described in US patent application publication No. 20050271641, and moisture absorbing polymeric material described in patent application EP 1187874, patent EP 1121190 and U.S. Pat. No. 6,174,952 or a multilayer plastic polymeric flexible packaging foil having a chemical desiccant material incorporated within a layer of foil as described in U.S. Pat. No. 8,003,179.
The description of the polymeric material in the above-mentioned patent documents includes processes and resulting structures for producing a modified polymer having interconnecting channels. The interconnecting channels act as controlled transmission passages through the polymer. A hydrophilic agent is blended into the polymer so that it is distributed within the polymer. A water-absorbing material is blended into the polymer so that the water-absorbing material is distributed within the product. The product is solidified so that the hydrophilic agent forms passages in the product through which a desired composition is communicable to the water-absorbing material that is entrained within the product. The solidified product described in above-mentioned patent documents may be used to form a desired shaped article such as plug type inserts and liners for closed containers, or it may be formed into a film, sheet, bead or pellet. One example of such a product is M-0026 Activ-Strip™, (CSP Technologies, Auburn, USA), which is a moisture absorbing film with molecular sieve.
However unlike the invention herein none of the prior-art, including the patent documents mentioned above, mention the absorption of moisture from a non-water liquid, including oil using a specific moisture absorbing material, such as especially prepared polymer strips or foils having an incorporated chemical desiccant material. On the contrary, it is clear from for example EP1187874 that this technology is intended for passage of a gas through the polymer.
Thus, it was previously known that the stability of probiotic lactic-acid producing cultures is closely correlated with water activity of the formulation, it was also known to dry oil under vacuum for the stabilization of lactobacilli. It was a surprise when the inventor of the invention herein showed that using specific desiccant material incorporated into a specific polymeric structure together with oil-formulated L. reuteri considerably improved the stability of such cultures.